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sansui 881 recap - filter cap bypass?

S

special_20

Active Member
In the midst of recapping my Sansui 881 amp. Stock the amp has 3.3 kohm resistors across the 10k uf main filter cap terminals. Most of my previous recaps have been marantz receivers and the group wisdom seems to be that they benefit from a bypass cap on the main filter caps.

Any benefit to adding additional lower value film bypass caps in parallel or as a replacement to these resistors in the Sansui? If so, what values would be appropriate? I know, I know, "if it ain't broke, don't fix it". But I'm equal parts wondering what is the theory on bypass caps is and morbidly curious how one might spec them?
 
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3.3K is low, i replaced a 150K 2W for a 300K 2W on a tube amp, for the 300V B+ rail.

This is Bleeder resistors, for protection, to discharge the capacitors slowly when not in use, to avoid an accidental discharge if you open the unit and not care about discharging capacitors.

For decoupling, try 2.2uf 630V CBB capacitors, faster, lower ESR than big lytics, and filter high pitch noise and interferences.
 
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3.3Kohm or 3.9Kohm is standard in Sansui gear for bleeder resistors - the voltage is lower so the lower value resistor is valid and correct.

mroboto said:
For decoupling, try 2.2uf 630V CBB capacitors, faster, lower ESR than big lytics, and filter high pitch noise and interferences.
Click to expand...

Agree.
 
Yes, lower voltage = lower bleeder value in most cases.

But you can jump a little higher in value, like 20K, jutst to keep something, for safety purpose,

A Sansui with ≈ 50V on the rail will probably not kill you as a tube amp can.

My amp power transformer seems to run a little bit cooler since he draws very little bit less current with 300K instead of 150K bleeder on my Raphaelite DP84.

The capacitors discharges quickly anyway.
 
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I did a lot of research on the question of bypass caps in parallel to the main supplies. I spend hours on DIYaudio.com as well as other sources. The conclusion was that adding by-pass caps have a) zero audible effect and b) potentially creates unintended effects. So I decided to take a listen using a highly resolving and rebuild Au-999, I put it sideways, removed the bottom plate and by using small alligator clips, was able to almost instantly remove the bypass. Result: absolutely no difference to my ear. I ended up leaving them out, following the old adage, Less is more. I am aware that some manufactures did use bypass, but that was 40 years ago. I don't believe new quality caps needs it. Just my 2 cents.
 
It seems to me that these capacitors, if fitted at all, should go on the driver boards or as close to the output transistors as possible. And maybe the lugs of the main PSU capacitors were just a convenient anchor point, very likely close to a main chassis ground.
 
Hyperion said:
It seems to me that these capacitors, if fitted at all, should go on the driver boards or as close to the output transistors as possible. And maybe the lugs of the main PSU capacitors were just a convenient anchor point, very likely close to a main chassis ground.
Click to expand...

That was exactly the consensus from some of the audio designers on DIYaudio - that if anything, those by-pass caps should be as close to the load as possible.
 
all right so bypass caps are either snake oil or a relic of another era of capacitor manufacturing seems to be the consensus. That and the size of cap you guys have recommended seem physically huge. I think I'll keep it running stock for the time being. Thanks!
 
Those caps may reduces the hiss you can hear if you put your ear close enough to the tweeter to ear something.

I bought a lot of 2.2uf 630V CBB to put in everything i work on and use, they are cheap enough to make some spares...
 
Mroboto is it 63v or 630v? The 630v Panasonic ecq caps are like an 1.5" by .75" which seems ginormous for a bypass cap. What brand are you using? I'm curious as to why such a high voltage spec or is that predicated on a tube amp with a higher rail voltage application?
 
No mistake - it is 630V, but 250V or 400V would be enough, such high voltage capacitors perform better when used well within their specification, it is a very common practice to use capacitors of similar voltage rating in these positions.
 
Yes, 630 V

Search on eBay typing CBB 2.2uf 630V and chose price + shipping lowest first

Voltage they can handle probably have no effect with decoupling caps, with coupling caps, i think the higher voltage caps tends to sounds more detailled.
 
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